1. Field of the Invention
The present invention relates to a control system for an adjustable focus lens in general, and to such a control system for an adjustable focus lens in a photographic camera, in particular.
2. Description of the Prior Art
Adjustable focus lenses and apparatus utilizing such lenses, such as photographic cameras, telescopes and the like are well known and their operation well understood in the prior art. A camera having an adjustable focus lens and having a focus control system coupled to said lens for automatically focusing image carrying light rays of a remote object at the film plane of said camera in response to a rangefinder derived signal representative of the actual distance between said camera and said remote object, are also known in the prior art. A camera having such a focus control system that utilizes acoustical energy to determine the distance to an object remote from said camera is described in U.S. Pat. No. 3,522,764 to BIBER, et al.
A bidirectional focus control system, i.e., a focus control system that, once commanded to do so, can move the movable element of an adjustable focus lens in either of two directions from any initial position within the normal focusing range of said lens, for focusing purposes, is also known in the prior art. One example of such a system is described in the above-mentioned BIBER et al. patent.
Another type of focus control system for an adjustable focus lens is sometimes referred to as a unidirectional focus control system in that the movable or focusing element of such a lens is always moved from the same or known reference point for focusing purposes. While such an element is movable in either of two axial directions, no lens focusing is performed as said element moves within its focusing range towards said reference point. A unidirectional focus control system of this type is significantly less complex than a bidirectional focus control system because it is unnecessary to continuously monitor lens element movement as said element is moved toward said known reference point. The cost savings attendant a unidirectional focus control system over a bidirectional focus control system makes the unidirectional focus control system attractive to the control system designer.
In my copending U.S. patent application Ser. No. 865,852, I disclosed a manual and a unidirectional automatic focus control system for a self-processing adjustable focus lens camera. For convenience, the specification in said application is specifically incorporated herein. In said unidirectional focus control system, the focus control mode is selected by switch means actuated by adjustable focus lens movement outside of the normal focusing range of said adjustable focus lens. The manual focus control mode is selected by manually moving said lens to any position within its normal focusing range. The automatic focus control mode of said control system is selected by actuating said switch means by either manually moving said adjustable focus lens to a predetermined position outside of its normal focusing range or, in another embodiment thereof, by taking a picture when said lens is within its normal focusing range which will cause the automatic focus control system to position said lens to said predetermined position after a picture has been taken and fully processed. Focus control mode selecting means that does not rely on lens position are not provided. Because lens movement and mode selection are so interrelated, and because separate focus control mode selecting means are not provided, a camera operator may fail to take note of lens position and incorrectly assume that the camera is in its automatic focus control mode at the beginning of a picture taking sequence which may result in the taking of at least one out-of-focus picture. Another potential problem is the possibility of a camera operator draining the camera's battery by leaving said camera in its manual focus control mode for an extended period of time. The nature of the control system in my above-cited patent application is such that leakage currents are drawn by the automatic focus control system when the manual focus mode is selected, and though relatively small, these leakage currents could be enough to render the camera's battery inoperative if the camera was left in its manual focus control mode and then stored for an extended period of time.